Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$172.77	7.254%	$185.3027	$185.30	$185.30	$185.30
Purchase #2	$106.54	13.284%	$120.6928	$120.69	$120.70	$120.70
Purchase #3	$158.29	10.757%	$175.3173	$175.32	$175.30	$175.30
Purchase #4	$188.30	5.459%	$198.5793	$198.58	$198.60	$198.60
Purchase #5	$237.81	10.708%	$263.2747	$263.27	$263.25	$263.30
Purchase #6	$190.56	4.110%	$198.392	$198.39	$198.40	$198.40
Purchase #7	$244.65	4.476%	$255.6005	$255.60	$255.60	$255.60
7 purchase totals =	$1,298.92		$1,397.1593	$1,397.15	$1,397.15	$1,397.20